Overload relief for electric motors



Sept. 15, 1953 J. L. MOODY ETAL 2,652,527

OVERLOAD RELIEF FOR ELECTRIC MOTORS Filed Jan. 13, 1950 4 Sheets-Sheet 1FIE-J mmvroxs. JOHN L. MoooY y ELwooo ADmns Sept. 15, 1953 J. L. MOODYETAL OVERLOAD RELIEF FOR ELECTRIC MOTORS 4 Sheets-Sheet 2 Filed Jan..13, 1950 s m s T NWV m N IMA D M H om .UE Y B Sept. 15, 1953 J. MOODYETAL OVERLOAD RELIEF FOR ELECTRIC MOTORS 4 Sheets-Sheet 3 Filed Jan. 13,1950 FIE-E Sept. 15, 1953 .1. MOODY ETAL OVERLOAD RELIEF FOR ELECTRICMOTORS Filed Jan. 13, 1950 4 Sheets-Sheet 4 INVENTORS.

Ewooo A. DAVIS Patented Sept. 15, 1953 OVERLOAD RELIEF FOR ELECTRICMOTORS John L. Moody, Oakland, and Elwood A. Davis,

Hayward, Calif.,' assignors to Friden Calculating Machine 00., Inc., acorporation of California Application January 13, 1950, Serial No.138,328

9 Claims.

This invention relates to an improved overload means for power drivenbusiness machines and the like, and more particularly to an arrangementfor automatically stopping the operation thereof by disconnecting thedriving motor from the power supply system whenever overload conditionsoccur as a result of improper operation of the machine.

In the design and construction of automatic business machines, such asautomatic calculators and the like, it has frequently been the practiceto provide some form of overload relief means between the driving motorand the power input shaft of the machine so as to avoid possible damageeither to the machine or to the motor in the event the resistance torotation becomes excessive. One arrangement which has sometimes beenused for this purpose utilizes a slip clutch which limits the torquetransmitted from the motor to the input shaft of the machine to apredetermined maximum value, and provides an audible warning to theoperator whenever this predetermined maximum value is exceeded, butwithout disconnecting the motor from the power supply. Such a warningdevice is often objectionable and disturbing to other workers,particularly if the business machine is used in a relatively congestedarea, since this audible warning normally persists until such time asthe driving motor of the machine is relatively quiet overload responsivemeans for a business machine or the like which is operable to open thepower circuit for the driving motor whenever the torque transmitted bythe motor exceeds a predetermined maximum.

It is another object of the invention to provide a readily adjustableand fully automatic slip clutch mechanism for a business machine, or thelike, which is responsive to predetermined overload values forinterrupting the driving motor power circuit in a business machine, orthe like, and without requiring attention on the part of the operator.

It is also an object of this invention to produce an overload responsivedevice adapted to automatically open the driving motor supply circuit ofa business machine, or the like, in the event the machine for any reasonbecomes inoperative or the resistance to rotation becomes excessivelyhigh, which device is capable of being manually reset so as to restorethe motor to 2 normal functional control after the disabling or overloadcondition has been eliminated.

It is still another object of the invention to provide an overloadresponsive mechanism operable to automatically stop the operation of thedriving motor in a business machine, or the like, without attention onthe part of the operator and in such a manner as to protect both themachine and the motor from possible damage during predetermined overloadconditions substantially impeding or preventing normal operation of themachine, which mechanism includes manually operable means forconditioning the motor control circuit for normal operation as soon asthe overload condition has been eliminated.

It is also an object of the invention to produce an overload responsivemechanism for automatically disconnecting the driving motor powercircuit in a business machine, or the like, in the event of jamming ormalfunctioning of the machine, which mechanism includes means foradjustably changing the critical value of torque for which the overloadresponsive mechanism is set, and is also provided with manually operablemeans for restoring the motor power circuit to normal functional controlafter the overload condition has been removed.

These, and other, objects of the present invention will be apparent fromconsideration of the specification and claims hereof, and by aconsideration of the drawings, in which:

Fig, 1 is a left-hand view of the right control plate showing theoverload responsive device and the resetting means therefor.

Fig. 2 is a right-hand View of the right control plate showing themechanism illustrated in Fig. 1.

Fig. 3 is a fragmentary elevational view to an enlarged scale showing atypical control key arrangement for a business machine.

Fig. i is a plan View of the motor control circuit and its associatedoverload responsive mechanism taken along the lines l l in Fig. 1.

Fig. 5 is an elevational view of the slip clutch mechanism takenalongthe lines 5-4: in Fig, 4 and looking in the direction of the arrows.

Fig. 6 is a front elevational View of the slip clutch taken along thelines 6-6 in Fig. 5.

Referring now more particularly to the drawings, in which like referencenumerals indicate like parts in the several views, there is showngenerally at 20 a right-hand control plate of a business machine, suchas an automatic calculator, which plate is suitably secured to the base2! of the machine and to the crossframe mem=- here 22, 23 (Fig. 1) whichtransversely extend across the bed of the machine. An electric motor 24,preferably of the series-wound or other suitable type, has one brushterminal 25 (Fig. 4) connected with a terminal 26 on a normallyopen,single-pole, single-throw, micro-switch 21 having its other terminal 28connected to one lead of a dual conductor power supply cord, the otherlead thereof being connected directly to the motor brush terminal 29.Motor 24 has a rotating armature which drives an output shaft 30 througha slip clutch 3|, the shaft 38 being extended through a suitableaperture in the plate 28 to carry a pinion gear 32 secured to the outerend thereof. This gear 32 is adapted to drive a larger diameter gear 33which rotates the clutch drive gear 34 and maindrlve shaft35, whichshaft is adapted to be driven through a main clutch 46 in the samedirection as the 'motor armature, but at a predetermined lower speeddetermined by the gear diameters.

Referring now to Fig. 3, there is shown a pair of control keys 36, 31,such as the minus and plus keys of an adding or calculating machine,each such key being slidably supported for predetermined verticalmovement by a pair of substantially vertically disposed and alignedelongated slots 38 which coact with a pair of corresponding screws 39carried by the supporting structure. Each such control key iscontinuously urged to its uppermost position by a suitable tensionspring, not shown, and adjacent the uppermost slot 38 on each key thereis provided a stud 48 adapted to coact with an angularly disposedcamming slot 4| formed in a longitudinally movable control slide 42supported for endwise sliding movement on the top pair of screws 39 bythe longitudinally disposed slots 43. A main clutch. control lever 44pivoted as at 45 (Fig. 2) actuates a conventional ratchet mechanismwhich is operable to establish a clutching engagement between the gear34 and the main drive shaft 35. A disk cam 58 on main clutch 48 coactswith a roller 41 carried by the. downwardly extending arm 46 to move thelever 44 clockwise as viewed in Fig. 2 so as to maintain the clutch 48in engagement. When the machine reaches the fullcycle positionillustrated in Fig. 2, however, roller 41 falls into an irregularity inthesurface of clutch cam 58, under the urgency of spring 49,

so as to move the main clutch 48 to its disengaged position. Since thestud 5| carried by the upper arm of clutch lever 44 projects outwardlyacross the rear edge of the control slide 42 (Fig. 3), the rearwardmovement imparted to slide 42 by a depression of either of the controlkeys 36, 31 rocks the control lever 44 (clockwise in Fig. 2) so as tomove the clutch mechanism out of its normally disengaged full-cycleposition. Stud 5| is also connected to one end of a link 52 having itsother end connected bya pin 53 with one end of a lever 54 pivoted as at55 on the control plate 28. The other end of lever 54 is pivotallyconheated at the point 56 with one end of a downwardly and rearwardlyextending switch control link 51.

As shown in Figs. 1 and 5, the link 51 is provided with a substantiallyU-shaped portion 58 adapted to pass below and in predetermined closeproximity to the slip clutch 3|, but without direct contact therewith.The control link 51 is also provided with a horizontally disposed rearend portion 59 which is supported for endwise sliding movement by therearwardly extending prong 60, the inner surface of which slideslongitudinally across the upper surface of a bolt, 01' pin, 6| suitablysecured to the control plate 28. This rearward end 59 of link 51 alsocarries a longitudinally extensible live finger, or switch actuatingmember, 64 supported for predetermined endwise sliding movement at therearward end of link 51 by the pin and slot connections provided by theoblong slots 65 and the supporting pins 66. This slidably supported livefinger, or tip, 64 is provided with a downwardly depending right-angleextension 61 adapted to coact with the actuator arm 68 of micro-switch21. The slidable switch actuating finger, or tip, 64 is provided at itsforward end with a lug, or ear, 69 adapted to coact with a latchingtooth 10 having a beveled outer surface 1|, which tooth 10 is formed onone end of a latching lever 12 pivoted as at 63 on the link 51 in aposition between slip clutch 3| and bolt 6|. The downwardly dependingtooth 18 of the lei/er 12 is urged into latching engagement with the lug69 by the downward resilient action of a spring 13 operably connected tolever 12 and anchored at its lower end to a pin 14 carried by the link51. The forwardly extending arm 15 of latching lever 12 is provided witha relatively large ear or right-angle extension 16 which is horizontallydisposed directly below the slip clutch 3| and in predetermined closeproximity with the lower surface thereof.

As shown in Fig. 6, there preferably is provided between armature shaft19 and slip clutch 3| 9. self-aligning coupling 88 consisting of aninner disk 8| driven by the armature shaft 19 and an outer driven disk83 separated from the driving disk 8| by a disk-shaped layer of leatheror other suitable flexible material. Disk 8| has a pair of pins 82projecting outwardly therefrom into coacting holes formed in theresilient disk 85, whereas the driven disk 83 establishes a torquetransmitting engagement with the disk 85 through the pins 84. Armatureshaft 19 extends through a centrally disposed hole in the disks 8| and85 and has its outer end rotatably seated against the driven disk 83.Secured to the disk 83 by the pins 86 is an outer clutch assembly 18which rotates with the disk 83 and includes a pair of oppositelydisposed clutch pawls 81 and an outer clutch plate 88. Extending througha centrally disposed aperture in plate 88 is a short cylindrical spindle9| whose inner end abuts against the outer surface of disk 83, whichspindle is freely rotatable in a suitable journal '92 secured to controlplate 20. Preferably, the output shaft 30, upon which the drive pinion32 is rigidly secured, is formed integral with spindle 9 I. Spindle 9|also has a pair of axially disposed and diametrically opposed V-grooves93 formed therein, which grooves are adapted to coact with the similarlyformed and substantially V-shaped latching projections 94 provided onthe free end of each clutch pawl 81. A pair of tension springs 95 eachhaving one end secured to a pawl supporting pin 86 and its other endaffixed to a pin 96 carried by the free end of the oppositely disposedpawl 81, resiliently urge the projections 94 on the pawls into one ofthe similarly shaped v grooves 93 provided on the coactin'g surface ofthe short spindle 9|. Thus, whenever torque in excess of a predeterminedmaximum value is transmitted by the motor armature 19'to the slip clutch3| through the self-aligning coupling 80, each pawl 81 on the slipclutch is forced outw ardly by the camming action of the projections 94as they are positively moved out of engage ment with the V-grooves 93 onspinal-e91 so that the contoured outer surface 91 of each pawl 81 movesoutwardly beyond the periphery of the disk 83, in opposition to theresilient action of spring 95, whereupon the pawls 81 move the latchinglever 12 clockwise as viewed in Fig. 5. In this manner, latch tooth IIIis released from engagement with lug 69 so that the extensible tip orlive link 64 is moved rearwardly to a second adjusted positiondetermined by the pin and slot connection between the members 51 and 64,which outward movement is imparted to the ex-- tensible link 64 by theoutward resilient action of the micro-switch actuator arm 68, the latterbeing continuously urged towards the open-circuit position(counterclockwise in Fig. 4) by a compression spring 98 contained withinthe micro-switch 21.

Means is provided for adjusting and changing the critical torque valuefor which the slip clutch 3| is set, and to equalize the torque settingsof the two clutch pawls 81 with each other. For this purpose there isprovided in the plate 88 a pair of radially disposed and diametricallyopposed slots I00, each of which carries a pin lflI (Figs. 5 and 6)which may be adjustably moved into and retained in a predeterminedpressing contact with the adjacent tension spring 95, thereby varyingthe amount of torque which will be required to move the pawl projections94 out of the coacting V-grooves 93 on spindle 3| so as to release theassociated motor switch control mechanism. Moreover, the pins IIlI canbe adjustably positioned within the slots I so that substantially thesame amount of torque will be required to simultaneously release both ofthe clutch pawls B1.

Mechanism is also provided for manually restoring the extensible link orlive tip 64 to its normal fixed position with respect to control link51, illustrated in Fig. 1, wherein the forward ear 69 on link 64 coactswith the beveled edge II on the latching lever 12 to re-establish alatching engagement between ear 69 and the downwardly depending tooth 10on the lever. During this forward movement of the slidably supportedlive tip or switch actuator 64 the downwardly depending arm 61 thereonrestores the micro switch 21 to its initial position by depressing theactuator 68 in opposition to the resilient action of spring 98. Thecontrol linkage provided for resetting and relatching the slidable tip64 may be utilized to perform other control functions in the machine, ifdesired, such as suspending or terminating the operation of an automaticcalculating machine during automatic division operations, and includes amanually operable slip clutch restore key I (see Fig. 2) pivoted as atI06 on plate 20 and provided at its rear end with a stud I01 adapted tocoact with one arm I08 of a bellcrank IIIl rotatably supported on a pinI09. The rearwardly extending arm of bellcrank IID coacts with a studIII carried by one arm II2 of a bellcrank H3 pivoted as at H4 on theright-hand control plate. Bellcrank I i3 has an upwardly extending armH5 which engages a pin I I! carried by a second bellcrank H8 pivotallysupported by the pin H4, Bellcrank H8, and consequently bellcrank H3, isurged in a counterclockwise direction by a suitable tension spring H6.Bellcrank IIB'has a rearwardly extending arm I I9 pivotally connected atthe point I20 to the upper end of a link I2I (see Fig. 1) pivotallyconnected by the pin I22 to one arm of a lever I23 rotatable about theaxis of a shaft I24 which projects outwardly beyond the control plate20. The other end of lever I23 is pivotally connected at the point I25to the upper end of a link I26 having its lower end connected by a pinI21 to one arm of a bellcrank I28 which isfree to turn about the axis ofa transverse shaft I29. The downwardly depending arm of bellcrank I28 isprovided with a flanged ear or lug I30 which is adapted to coact withthe downwardly depending right angle extension 61 on the extensible linkor live pawl 64 so as to depress the microswitch-actuator 68 and returnthe switch actuating finger 64 to the normally retracted positionillustrated in Fig. 1.

It will be readily apparent from the foregoing thatthere has beenprovided a slip clutch arrangement which can be readily adjusted forvarying degrees of overload so as to prevent either the driving motor orthe business machine driven thereby from being damaged inthe event ofjamming or improper'functioning 0f the machine. There has also beenprovidedan-overload responsive motor switch control mechanism which isoperable to supersede or override the normal functional controls andautomatically open the motor power supply circuit whenever the torquqedelivered by the motor output shaft exceeds a predetermined maximum,which mechanism is relatively quiet in its operation and is readilyre-engaged for normal functional control as soon as the abnormalcondition responsible for the overload has been eliminated. Moreover, anoverload responsive mechanism has been provided for automaticallydisconnecting the driving motor supply without requiring action on thepart of the operator or creating an audible warning which may bedisturbing to other personnel working in a relatively congested area.

We claim:

1. An overload relief device for a motor which comprises the combinationof a clutch disk driven by the said motor, a plurality of pawls carriedby the said disk, resilient means biasing said pawls to a retractedposition, means for adjustably changing the resilient pressure tendingto urge the said pawls to their normally retracted position, a drivenshaft having a plurality of longitudinally disposed V-grooves thereonadapted to form a predetermined torque transmitting engagement with thesaid pawls, each of the said pawls being adapted to be moved outwardlybeyond the periphery of the said disk to anactive position whenever theresistance to rotation of the said driven shaft exceeds a predeterminedoverload value, a normally open power supply control switch for the saidmotor, a switch control member, and a latch operable to releasablyretain the said switch control member in the closed circuit position,the said latch being released by the movement of the said pawls fromtheir normally retracted to their outwardly extending active position soas to open the said switch and automatically stop the said motor,

2; In a business machine driven by an electric motor and having anormally open power supply switch for controlling operation of themotor, the combination which comprises a power input shaft for the saidmachine, a slip clutch between the said motor and the said input shafthaving a plurality of normally retracted cams thereon adapted to bepositively expanded in response to a predetermined overload condition,means for adjustably setting the said slip clutch for varying conditionsof overload, linkage means including a retractable live link member foroperating the said switch, means for normally latching the said livelink member in a first adjusted position relative to the said linkagemeans, the said cams being operable in their expanded condition forreleasing the said link member for movement to a second adjustedposition in such a manner as to allow the said switch to move to theopen circuit position, and manually operable means for resetting thesaid link member in its first adjusted position after the said overloadcondition has been eliminated.

3. An overload relief device for an electric motor comprising thecombination of a driving member connected to said motor, a driven memberassociated with said driving member, notches in one of said members, aspring-urged pawl mounted on the other of said members normally engagingthe notches of the said one member, a normally open switch controllingthe flow of power to said motor, a control mechanism including a livetip adapted to be releasably latched in an operative position so, as toclose the said normally open switch, means controlled by thedisplacement of said pawl from said notch for releasing the said livetip for movement to a second position so as to cause the said switch tomove to its normally open position, and manually operable means forreturning the said live tip to its first position.

4. In a device of the character described, a motor, a driving memberconnected to said motor, a driven member associated with said drivingmember, a notch in one of said members, a pawl mounted on the other ofsaid members adapted to engage the notch of the said one member, anadjustable resilient means urging said pawl into saidnotch, a normallyopen switch controlling the flow of power to said motor, a manuallyonerated means including a switch control link and means for holdingsaid link in operative position for a predetermined cycle of operation,a live tip on said link engaging said switch, a latch for holding saidlive tip in switch closing position, means controlled by thedisplacement of said pawl from said notch for releasing said latch, anda second manually operated means for relatching said live tip in switchclosing position.

5. An overload relief device for a motor driven business machineincluding a control key and a motor switch, comprising a driving memberconnected to said motor, a driven member associated with said drivingmember, notches in said driven member, spring-urged pawls mounted onsaid driving member and adapted to engage the notches in said drivenmember, control linkage means normally operated by the said control keyand including a longitudinally slidable finger adapted to open and closethe said switch, and a latching lever operable to normally retain thesaid slidable finger in a switch closing position for movement with thesaid linkage means and to release the said finger for movement to aswitch opening position, the said pawls being operable upon thedisplacement from said notches to release the said latching member toopen the said switch independently of the position of the said controllinkage.

6. An overload device for a business machine having an electric motorand a normally open power switch for said motor, a drive shaft connectedto said motor, a driven shaft associated with said drive shaft, notchesin one of said shafts, springmrged pawls mounted on the other of saidshafts normally engaging the notches of the said one shaft, linkagemeans including a live tip slidably supported thereon for controllingoperation of the said switch, a latch normally latching the live tipoperatively to said linkage means, and means actuated by the outwardlydisplaced pawls for automatically releasing the said latch, whereby theswitch is permitted to move to its normally open position independentlyof the control exercised thereon by the said. linkage means.

7. In a device of the character described, a motor, a driving memberconnected to said motor, a driven member associated with said. drivingmember, notches in one of said members, a pawl mounted on the other ofsaid members, resilient biasing means urging said pawl into engagementwith the notch of the said one member, a switch controlling the how ofpower to said motor, and means controlled by the displacement of saidpawl from said notch for opening said switch.

8. In a device of the character described, a motor, a switch controllingthe flow of power to said motor, a driving member connected to saidmotor, a driven member associated with said driving member, and ayieldable connection between said driving and driven members comprisinga notch in said driven member, a pawl mounted on said driving member andadapted to, the notched driven member, a spring urging said pawl intoengagement with said notch, and means operated by movement of said pawlout of said notch for opening said switch.

9. An overload mechanism for a business machine driven by an electricmotor and having a normally open power supply switch for controllingoperation of the motor which comprises a power input shalt for the saidmachine, a slip clutch member between the said motor and the said inputshaft having a plurality of normally retracted cams thereon adapted tobe positively expanded in response to a predetermined overloadcondition, linkage means including a retractable live link member foroperating the said switch, latch means for normally latching the saidlive link member in a first adjusted position relative to the saidlinkage means and for releasing the said live link member for movementto a second adjusted position upon displacement of said cams from theirretracted position to move to the open circuit position, and manuallyoperable means for resetting the said live link member in its firstadjusted position independently of said linkage means.

JOHN L. MOODY. ELWOOD A. DAVIS.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 1,996,312 Tremolada Apr. 2, 1935 2,004,282 Horton u June 11,1935 2,062,905 Hilty et al. Dec. 1, 1936 2,203,233 Panish June 4, 19402,536,319 Slack g Jan. 2, 1951

